In the past, as shown in JP-A-2001-74283, the following configuration is proposed: an indoor unit of an air conditioner having a refrigerant circuit through which a combustible refrigerant circulates and a ventilation fan (ventilator) are installed in a room space (space to be air-conditioned), and when leak of combustible refrigerant is detected, the ventilator is operated to discharge the combustible refrigerant from the space to be air-conditioned.